The legend relates that Eustachius (before baptism, Placidus), a Roman general under Trajan, while still a heathen, saw a stag coming towards him, with a crucifix between its horns; he heard a voice telling him that he was to suffer much for Christ’s sake. He received baptism, together with his wife Tatiana (or Trajana, after baptism Theopista) and his sons, Agapius and Theopistus. The place of the vision is said to have been Guadagnolo, between Tibur and Praeneste (Tivoli and Palestrina), in the vicinity of Rome. Through adverse fortune the family was scattered, but later reunited. For refusing to sacrifice to the idols after a victory, they suffered death in a heated brazen bull. Baronius would identify him with Placidus mentioned by Josephus Flavius as a general under Titus.
The Acts are certainly fabulous, and recall the similar story in the Clementine Recognitions. They are a production of the seventh century, and were used by St. John Damascene, but the veneration of the saint is very old in both the Greek and Latin Churches. He is honoured as one of the Holy Helpers, is invoked in difficult situations, and is patron of the city of Madrid and of hunters. The church of Sant’ Eustachio in Rome, title of a cardinal-deacon, existed in 827, according to the Liber Pontificalis, but perhaps as early as the time of Gregory the Great (died in 604). It claims to possess the relics of the saint, some of which are said to be at St-Denis and at St-Eustache in Paris. An island in the Lesser Canilles and a city in Canada bear his name.